This invention relates to an apparatus and method for effecting the separation of items with different terminal velocities, such as sugar cane billets and leaf, as achieved in cane harvesters. In particular, it relates to the use of air flows of differing velocities to separate leaf and other trash from sugar cane billets.
Various mechanisms are known whereby separations, such as the separation of billets of sugar cane from leaves, tops and other trash picked up by a harvester, are achieved. For sugar production it is desirable to efficiently separate sugar billets from other matter so as to deliver a clean product to sugar mills for crushing.
This separation has typically been attempted, albeit somewhat ineffectively, in cane harvesters during harvest. In most known arrangements a flow of air is drawn through the cane as it passes through the harvester. One such arrangement is described in Australian Patent No. 569800 in the name of Claas OHG. This patent describes a separation process wherein harvested cane is carried up an inclined belt conveyor. At the end of the conveyor the cane and other material falls onto a transverse conveyor. Air is blown through the falling cane to separate lighter material from the heavier cane billets. A suction fan is mounted above the conveyor belt to assist with ejection of the separated material.
The Claas approach fails to achieve efficient separation at acceptable harvesting rates. Leaf is caught between cane billets and retained while some billets are discharged with leaf material. A more efficient approach is required.
In other approaches air is drawn through a moving bed of cane to separate cane billets from trash. Successful separation depends on utilising the difference in terminal velocity of a billet (typically 20 m/s) and other inclusions to the harvested cane such as tops (typical terminal velocity of 15 m/s) and leaves (typically 5 m/s). The usual configuration in a harvester is with a fan drawing air through the cane bed. Commonly used fans do not provide a uniform velocity profile over the whole treatment area. Uniformity of air flow is greatly affected by the air inlet conditions and geometry of the chamber in which the separation is effected and other factors including the presence and properties of the cane bed itself. Consequently, such means of separating trash from cane billets have not proven efficient because they result in a loss of cane billets ejected with the trash from some parts of the treatment area and the retention of trash in other parts.
Another approach to cleaning trash from cane billets is a modification of the Claas approach described above. A jet of air is blown through a curtain of falling cane to eject the trash. This configuration enables better control over air velocity and hence improved efficiency of separation. However, there is still room for improvement in the quality of the end product and in minimising loss of cane billets. Furthermore, the rate of processing must be increased to match the increase in harvesting speed with modern harvesters.
All of the above described methods cause a loss of cane when applied to billets in a cane harvester, and additionally they fail to remove sufficient extraneous matter. Cane is lost because it becomes entrained with leaf material or it is projected into the fan blades. Leaf can be trapped by the billets and not removed. Variation in density of the cane bed can cause zones where the air velocity is impeded and reduced and the effectiveness of the flow as a separation mechanism at these zones is consequently reduced.
It is an object of the present invention to provide an apparatus and method to improve the efficiency and effectiveness of the separation of objects, items, components, and the like, into distinct classes characterised by terminal velocity.
It is a further object of the invention to substantially ameliorate one or more of the identified shortcomings in the known prior art.
Further objects will be evident from the following description.
In one aspect the present invention provides an apparatus for separation of components having differing terminal velocities, including means for providing an upwardly projected air flow, said air flow acting to agitate, sort and separate said components according to a terminal velocity of each of said components, means for forming a bed of said components above said upwardly projected air flow, means for entraining a class of said components out of the bed, said means for providing said upwardly directed air flow including a narrow, elongate jet means extending substantially across said bed of said components.
In one form of the invention the bed of components is formed by projecting the components into and through the upwardly projected airflow. In another form of the invention, the components are distributed on a conveyor means which carries the components through the upwardly projected airflow.
In preference the apparatus further comprises a separation zone formed in the bed of components by the flow of air whereat components are distributed according to terminal velocity with lower terminal velocity components displaced upwardly with respect to higher terminal velocity components.
The components may be definable in classes wherein each class has a characteristic terminal velocity, and the terminal velocities of the components in the class are distributed about a mean value which is the characteristic terminal velocity.
In preference the means for entraining a class of said components is a low speed fan drawing an entraining air flow away from the bed of components, said entraining air flow entraining low terminal velocity components. The entraining air flow preferably acts throughout and/or adjacent the separation zone.
The upwardly projected flow of air and the entraining air flow act cooperatively to sort and segregate classes of components.
In preference the upwardly projected air flow has a velocity of between 20 m/s and 60 m/s and preferably in the range 30 m/s and 50 m/s. Most preferably the velocity of the upwardly projected air flow is 40 m/s.
The entraining air flow preferably has a velocity of between 2 m/s and 20 m/s. Most preferably the velocity of the entraining air flow is 12 m/s.
In a second aspect the present invention is a self-propelled harvester comprising cutting and gathering means at a forward end of the harvester; chopping means adjacent the cutting and gathering means for chopping harvested cane into billets and trash; means for projecting said billets and trash into a separation zone; separation means as defined above providing at least one narrow, upwardly projected air flow through the separation zone, said air flow acting to agitate, sort and separate the billets and trash, said entraining means entraining the trash out of the separation zone.
In one form the chopping means and the means for projecting said billets and trash into a separation zone are a single means such that the billets and trash are projected into the separation zone immediately after chopping.
The harvester may suitably include conveyor means adjacent the projection means, said billets and trash forming a bed on the conveyor means. In preference the conveyor means conveys the bed of billets and trash through the upwardly projected air flow. The conveyor means suitably comprises a belt of open mesh material.
Alternatively, the projection means forms an unsupported bed in the separation zone.
The means for entraining the trash out of the bed is suitably a low speed fan drawing an entraining air flow from the bed at a velocity sufficient to entrain the trash. The low speed fan is suitably located downstream of the upwardly projected air flow.